diff --git a/tcl/target/max32520.cfg b/tcl/target/max32520.cfg
index 8324da6724e22789d13d64f527775caf4fb0da29..710c3d4aef90cff8df9d3fe9bee8086ffaceb42f 100644
--- a/tcl/target/max32520.cfg
+++ b/tcl/target/max32520.cfg
@@ -17,3 +17,13 @@ set FLASH_CLK 40
 set FLASH_OPTIONS 0x23
 
 source [find target/max32xxx.cfg]
+
+proc max32520_aes256_reset_init {} {
+    # Enable encryption and 256 bit key
+    mww 0x40000000 0x320002
+}
+
+# Create custom reset sequence to set the AES keysize
+if { [expr $FLASH_OPTIONS & 0x40] } {
+    $_CHIPNAME.cpu configure -event reset-init { max32520_aes256_reset_init }
+}